The present invention relates to a network policing method for cell tagging within a communications network as described in the preamble of claim 1 and related device as described in the preamble of claim 2.
Such a cell tagging method is already known in the art, e.g. from the section xe2x80x9cTraffic and Congestion Control in ATM Networksxe2x80x9d, pages 302-340 in Asynchronous Transfer Mode: Solution for Broadband ISDN, third edition, from the author Martin de Prycker. Therein, a cell based traffic policing method called Usage Parameter Control (UPC), containing the steps of checking cells called determining cells to be conforming or non-conforming and tagging cells called cell tagging is described.
Since in a cell based tagging method only single cells from a frame are tagged, the frame may exist of a mix of tagged and non-tagged cells. In case of congestion the tagged cells might be discarded from the frame leaving incomplete frames in the network. Since incomplete frames are useless from an application point of view, hence the presence of these frames decreases network throughput.
This situation can be improved by using frame based traffic policing methods but, these often have the disadvantage that a number of cells of the entire frame which should be tagged, already have left the traffic policer. Only the cells that still remain within the traffic policer can be tagged. A frame exist of a mix of tagged and non-tagged cells is left then in the communications network. In case of congestion the tagged cells might be discarded from the frame leaving incomplete frames in the network. If such incomplete frames are not used anywhere in the communication network, then again the presence of these frames decreases network throughput.
As a remark on this frame based policing methods it should be mentioned that there are frame based policing algorithms possible and available not having the disadvantage of leaving corrupted frames within the network. One of those methods is described in the U.S. Pat. No. 5.666.353 with title xe2x80x9cFrame based traffic policing for a digital switchxe2x80x9d. However the disadvantage of this kind of methods is that the network has to support this method throughout the entire network to avoid incomplete frames within the network. This is very unlikely in the near future because it should be agreed and supported by all network operators.
Summarising the former, it can be said that applying traffic policing methods in a communication network in general, involves that the frames within the communication network may be incomplete because of a number of different possible problems as mentioned before. If such incomplete frames are not used anywhere in the communication network, then the presence of these frames decreases network throughput.
An object of the present invention is to provide a cell tagging method of the above known type and related devices adapted to perform this method, but wherein the network throughput is improved.
According to the invention, this object is achieved by the method described in claim 1 and the network buffer described in claim 2.
Indeed by determining a tagged cell distribution within a frame by the network buffer a decision on the distribution of tagged cells within this frame can be made. Based on this decision all cells of the entire frame can be marked with a low or high cell loss priority. In this way the network only transports frames consisting of tagged cells only or non-tagged cells only. If all cells have the same cell loss priority, the entire frame will be passed or discarded in case of congestion. In case of congestion within the network, no incomplete frames are transported through the network. Network resources consequently are no longer occupied by incomplete frames that are not used.
The above and other objects and features of the invention will become more apparent and the invention itself will be best understood by referring to the following description of an embodiment taken in conjunction with the accompanying drawing that represents, for the present invention, a relevant part of a Telecommunications network wherein a method for cell tagging according to the present invention is applied. The part of the telecommunications network drawn in the figure comprises a traffic policer TP and a network buffer NB which are interconnected and along which a communications path is set-up.